1. The Field of the Invention
The present invention relates to novel hydraulically bonded cement compositions and methods having low density. More particularly, the present invention is directed to incorporating solid removable aggregates into powdered cement which later dissolve, evaporate, volatilize, or melt leaving voids in the cement composition.
3. Technology Review
Hydraulic cements have been used for thousands of years as the binding agent in mortars and concretes. These cement-based materials are formed by mixing hydraulic cement, which is a dry powder, with water and often, either simultaneously or subsequently, some sort of aggregate is blended into the mixture. When water is added to hydraulic cements, the existing minerals in the cement either decompose or combine with water, and a new phase, such as a calcium-silicate-hydrate structure, grows throughout the volume. Upon curing, the water-cement mixture, sometimes referred to as cement paste, binds aggregates together to form concrete and mortar. The amount of water mixed with the cement and the intensity of mixing are often carefully controlled to maximize the ultimate properties while at the same time imparting desirable rheological properties to the cement paste.
By its nature, cement has historically been mixed with water and then shaped, formed, or placed in a mold. It has long been known that higher strengths can be achieved by reducing the water to solids ratio, but this has always had the disadvantage of making the mixture more stiff and difficult to place into a mold. Thus, the practical use of cement-based materials represents a compromise between having a workable fluid mixture, which requires excess water between cement particles, and having a very strong product, which requires dense packing of the cement particles. It is a compromise between two opposing requirements: that the cement paste be fluid and that the final product be dense and strong.
Most of the advances in cement science over the last ten years have been dedicated to overcoming the compromise between rheological properties and strength and density properties of cements. Efforts have been made to prepare a cement paste that is fluid enough to be handled, but that will react and form a dense final product. A number of surfactants, lubricants, and mixing techniques have been proposed to enable the cement paste to be manipulated early on and then later form a strong material.
In many applications, it is desirable to have a low density cementitious product having reasonably high strength. Such applications include insulation, lightweight structural components, products with controlled dielectric properties, and packaging.
From the foregoing, it will be appreciated that what is needed in the art are novel compositions and methods of hydrating hydraulic cement in which the cement can be readily manipulated, shaped, and formed into a strong, low density material.
Additionally, it would be a significant advancement in the art to provide novel compositions and methods of hydrating hydraulic cement in which the cement can be readily manipulated, shaded, and formed without first mechanically mixing the cement with water to form a cement paste.
Such hydraulic cement compositions and methods are disclosed and claimed herein.